Oil recovered from castor seed (Ricinus communis L.) is an important raw material in many industrial processes and/or syntheses due to its high content (i.e., in the range of 80%-90%) of the hydroxy fatty acid (HFA) ricinoleic acid (Eq 1).

The highly reactive hydroxy groups can be engaged in various chemical reactions and result in diverse end products such as lubricants, coatings and pharmaceuticals. For example, after recovery from castor oil, ricinoleic acid may be further converted to sebacic acid and capryl alcohol. Sebacic acid can be polymerized with hexamethylene diisocyanate to produce nylon-6,10. Capryl alcohol can be used in the production of plasticizers. Dehydration of ricinoleic acid, which occurs at the hydroxyl group, produces conjugated double bond structures. Accordingly, ricinoleic acids can be used as semi-drying oils.
However, castor plants and their seeds contain ricin and ricinine that are extremely toxic to many organisms including mammals, avian species and marine life. Consequently, there are significant safety concerns associated with the harvesting and processing of castor seed crops to produce oil.
One strategy to overcome the disadvantages of working with castor seed and castor oil has been to genetically modify other types of oil-seed plants to produce ricinoleic acid. However, it has been found that in comparison to castor seed, such genetically transformed plants typically produce very low levels of ricinoleic acid. As a result, considerable efforts and expense are required to recover, purify and enrich ricinoleic acid and other HFA from source oils produced from genetically modified plants.
It is possible to recover the hydroxy fatty acids lesquerolic acid (14-hydroxy-11-eicosenoic acid) and auricolic acid (14-hydroxy-11,17-eicosadienoic acid) from Lesquerella fendleri and Lesquerella gordonii oils by a process incorporating low-temperature crystallization. Lesquerella oils are first hydrolyzed for 3 hours then acidified to obtain free fatty acids (FFA). The FFA are then extracted with hexane, washed with phosphate buffer and dried to recover the FFA. The FFA are then dissolved in hexane and chilled to −25° C. overnight to allow crystallization and separation of the HFA. Finally, HFA are filtered, washed and dried. Although this method enriched lesquerolic acid and auricolic acid from 55-59% to 85-99% with 94% yield, the process required large amounts of solvents, long processing times and carefully controlled processing temperatures (i.e. −25° C.).
Another method to isolate HFA from source oils is based on salt solubility fractionation. Potassium salts of ricinoleic acid are isolated from castor oil by their different solubilities in different solvent systems at certain temperatures. However, in addition to the complexity of the process, the method is not effective for the separation of ricinoleic acid from oleic acid and linoleic acid.
Other strategies assessed separation and recovery of HFA from source oils based on urea fractionation of the fatty acids. However, it was found that this approach is more useful for the separation and recovery of polyunsaturated fatty acids (PUFA) rather than HFA.
Other methods for recovery of HFA from source oils incorporate liquid-liquid extraction steps. These approaches are based on the polarities of FFA/FAME and their solubilities in bi-phase solvent systems. However, these processes are complex and require large amounts of solvents and long processing times.